1. Technical Field
The present invention relates to an integrated circuit device that generates a drive voltage waveform (hereinafter simply referred to as a “drive waveform”) used for drive of an electrooptic panel such as an electrophoretic display (EPD) panel, and an electronic apparatus equipped with such an integrated circuit device. The invention further relates to a control method for an electrooptic panel.
2. Related Art
As a display device that achieves further more reduction in thickness and power consumption than a liquid crystal display device and a plasma display device, a display device using an EPD panel, etc., also called electronic paper, has been developed, and is being used in an electronic apparatus such as a wristwatch, an electronic book, an electronic newspaper, an electronic advertising signboard, and a guideboard.
In an EPD panel, for example, an electrophoretic layer is formed between a transparent top plane electrode provided on a surface layer and a plurality of segment electrodes provided on a bottom layer. The electrophoretic layer includes microcapsules each housing white electrophoretic particles and black electrophoretic particles charged to different polarities and a dispersion medium (transparent oil, etc.) for dispersing the particles.
By applying a voltage between the top plane electrode and a segment electrode to apply an electric field on the electrophoretic particles, the electrophoretic particles move depending on the direction of the electric field, thereby displaying the color of a pixel corresponding to the segment electrode. The EPD panel has a nonvolatile (memory) property in which, once an electric field is applied to electrophoretic particles to put the panel in a display state, the display state is maintained thereafter with no electric field being applied to the electrophoretic particles. Therefore, since it is only necessary to apply an electric field to the electrophoretic particles when display is first performed and when the contents of the display are changed or deleted, wide power savings can be made.
In driving the EPD panel, the voltages applied between the top plane electrode and the segment electrodes are changed in accordance with their drive waveforms during the time until the display state of the EPD panel changes from a first display state corresponding to first display data to a second display state corresponding to second display data, thereby stabilizing the display state.
To achieve the above, a display device using an electrooptic panel such as the EPD panel uses an integrated circuit device (display controller or display driver) that sets drive waveforms used for driving the electrooptic panel, or sets drive waveforms and drives the electrooptic panel. Also, since the characteristics of the EPD panel are sensitive to temperature, the drive waveforms are compensated in response to a change in temperature.
As related technology, JP-A-2007-508595 (Abstract, Table 1: Patent Document 1) discloses a method and system that control electrophoretic and other bistable displays. Coded data for different pixel transitions and different temperatures for driving a display is stored in memory (LUT1 to LUT15, etc.). The coded data has voltage levels and timing information for different pixel transitions. Part of the coded data is retrieved by a controller based on selected pixel transition, temperature, and updated mode. Part of the coded data including a fixed-length frame instruction is decoded, and the decoded data provides a voltage waveform for driving the display.
JP-A-2012-53084 (para. 0007-0008, FIG. 6: Patent Document 2) discloses an integrated circuit device that easily responds to a plurality of drive styles in driving an electrooptic panel such as an EPD panel. This integrated circuit device includes a drive voltage generation section that outputs a drive voltage supplied to a segment electrode of the electrooptic panel, a display data memory section that stores at least first display data and second display data, and a drive waveform information output section that outputs drive waveform information at the time when the display state of the segment electrode changes from a first display state corresponding to the first display data to a second display state corresponding to the first display data.
The drive waveform information output section has a first memory section that stores drive waveform information in each of basic periods T1 to TM (M is an integer equal to or more than 2), a second memory section that stores a first designated period designating at least one basic period out of the basic periods T1 to TM and a first number of times of repetition of the first designated period, and an output section that outputs drive waveform information corresponding to each of the basic periods T1 to TM, the first designated period, and the periods specified by the first number of times of repetition. The drive voltage generation section outputs a drive voltage specified by the first and second display data from the display data memory section and the drive waveform information from the drive waveform information output section.
Japanese Patent No. 5,293,532 (para. 0006-0011, FIG. 6: Patent Document 3) discloses an integrated circuit device that permits sequential drive of an electrooptic panel while seeking to reduce the processing load on a control device. In this integrated circuit device, a drive waveform information output section includes registers RT1 to RTM (M is an integer equal to or more than 2), where a register RTk (1≤k≤M) out of the registers RT1 to RTM stores a register value specifying the signal level of a drive waveform signal during a period Tk out of the periods T1 to TM and a period length register value for setting the length of the period Tk.
During a period Tp (1≤p≤M−1) out of the periods T1 to TM, the drive waveform information output section sets the length of the period Tp based on the period length register value from a register RTp, and outputs a register value specifying the signal level from the register RTp. During a period Tp+1 subsequent to the period Tp, the drive waveform information output section sets the length of the period Tp+1 based on the period length register value from the register RTp+1 and outputs a register value specifying the signal level from the register RTp+1.
In Patent Document 1, where temperature-specific look-up tables (LUTs) (see Table 1 in Patent Document 1) are used, the same number of LUTs as the number of temperature ranges for which different drive waveforms are used is required, and thus a large data area is necessary to store such LUTs. In Patent Documents 2 and 3, it is necessary to store data representing the length of a period (the period length register value) for each period during which the drive voltage is output, and thus a large data area is necessary to store such data.
Moreover, in Patent Documents 2 and 3, data such as the start and end periods of output of the drive voltage or the number of times of repetition must be held separately. In order to perform temperature compensation of the drive waveform, therefore, there arises a trouble of rewriting such data every time the temperature range changes. It may be possible to secure a data area where all data for the different temperature ranges is stored and select appropriate data according to a temperature range. This however raises a problem of further increasing the data area.